Method for desuperheating steam



Aug. 12,. 1930. v .1.42, MCDERMET 1,773,053

I Y METHOD FOR DESUPERHETING STEAM Filed July 1s, 192s Figi Y 10Tolla-'Ar.afwas/,154615K INVENTOR Patented Aug. 12, 1930 UNITED .STATESPATENT-OFFICE" JOHN It. MCDERMET, 0F J' EANNETT E,l PENNSYLVANIA,ASSIGNOR T0 ELLIOTT COI- PANY, 0F PITTSBURGH, PENNSYLVANIA, ACORIL'ORATION 0F PENNSYLVANIA METHOD FOR DESUPERHEATING STEAMApplication 1ed July 13,

The present invention relates broadly to power plant equipment, and moreparticularly to a method for desuperheating steam. In accordance lwiththis invention, the superheated steam is treated, whereby it is adaptedfor heating purposes.

With the increase of steam pressures and superheat in power stationpractice, the exhaust steam from auxiliary turbines and the like isbecoming highly superheated, sometimes as much as 200. This isoccasioned by the initial high energy content of the steam beforeentering the turbine, due-to the increase of superheat and pressures,and also partly to the relative ineiiciency of small turbines, theseturbines being ordinarily proportioned for economic considerations otherthan very high heat economy.

The same situation exists with steam discharged from the gland seals oflarge turbines,-this steam having been used for sealing urposes andthrottled from the condition of initial high superheat 'and pressure toapproximately atmospheric conditions.

As a matter of technical fact, the superheated steam has only aboutone-thirtieth the conductivity of saturated steam from the standpoint ofheater performance. It is well known that the major transfer of heat inheater condensation is from the latent heat of the steam in condensing.In the case of under the usual conditions of operation.

In the average closed feed water heater, the superheat is destroyed tosome. extent by the condensation which ultimately forms on the tubes,due to the removal of heat; and the value one-thirtieth, before referredto, for performancepmay, therefore, not be the lactual valueobtained inpractice.. It is, however, a practical fact vthat it is almostimpossible-to use superheated steam eiic'iently from a heatingstandpoint in closed heaters. It 1s neces- 1923. Serial No. 651,801.

sary to provide suiiicientsurface within the heater and such conditionsas to permitv the condensate which ultimately forms in the heater, dueto the removal of heat, to act asa desuperheating medium.

From the foregoing, it becomes ap arent that much more effective resultscould e obtained ifit were possible to desuperheat the steam before itspassage to the heater, and thereby render the latent heat available .for

use. The present invention relates to such a desuperheating and providesmeans for eiliciently producing the results desired by reducing thesuperheated steam to a saturated condition by intimately mixing watertherewith. In this process, an amount of water equivalent `to thesuperheat of the steam is evaporated in the desuperheater, and the sameheat quantity, under the same pressure conditions goes into the heater,but under a condition of saturation and with an increased amount ofsteam, due to the evaporation in the desuperheater. ,c Y

I have found that spraying water into the path of superheated steam isnot a very effective means of desuperheating. haps primarily because ofdifficulty in suiciently atomizing the water to intimately mingle itwith the steam, and still retain it within the body of thedesuperheater. It is not eilicient, in general, to allow water from thedesuperheater to low over irto the heater, as water, it being desirablethat it go over as saturated vapor. Ihave also found that heat transfertakes place more readily from steam to metal when the metal is coveredwith water than from a spra as referred to. lThis is probably due to t eincreased time limit in which the water and steam are in Contact.Thepresent invention, therefore, involves the treatment of thesuperheated steam under ideal conditions for the evaporation of thetreating water and for the reduction of the This is persuperheat in thesteam to a conditionof saturation. l In the accompanyi drawin there 1sunderstood that the drawings do not define `through the apparatusillustrated in Figure l.

In accordance with the present invention, superheated steam from anydesired source may be conducted to the desuperheater through an inlet 2.This inlet is in communication, as clearly shown in Figure 2,

with the interior of the desuperheating chamber 3. In order to passthrough this chamber to the outlet 4, it is necessary for the steam tofirst pass through the baille 5,the wire mesh 6, and the baille 7. Thesebaflles may advantageously be constructed of perforated Monel metal andthe wire mesh 6 therebetween may be of Monel spacer cloth loosely wovenof interlocked Monel wire, al\

though other materials may be used, if desired. Preferably the wire meshis in the form of a ribbon of material having a Width substantialy equalto the width of the chamber 3, and adapted to be inserted between theperforated plates by permitting the same to fold over upon itself, asclearly indicated in the drawings. Due to this construction, the bailleplates and the wire mesh form, in effect, a cartridge which can bebodily inserted in or removed from the chamber 3.y To facilitate suchinsertion and removal, the chamber may be provided with a removable head8.

Carried by the head 8 is a water manifold 9, having anv inlet connection10 leading to a suitable source of water supply and provided with aseries of discharge outlets or nozzles 11` extenfin substantially acrossthe removable cartri( ge. These nozzles distribute the water uniformlyover the wire mesh, so that it runs slowly thereover, but any excess notevaporated by the superheated steam is discharged through a suitableoutlet 12 in the bottom of the desuperheater chamber.

It will be apparent that the steam is effectively broken up and broughtinto intimate contact with a largearea of metal surface covered withwater, thereby providingl a very eflicient means for reducingsuperheated steam to a condition of-saturation. The steam increased inquantity, due to the evaporation ofthe water supplied fordesuperheating, but containing the same heat content under the samepressure conditions` then passes through the outlet connection. 4, to asuitable heater, not shown. This apparatus provides for a transfer ofheatpartly direct from the steam to the water 1n the slow process of theflow of water through the apparatus, and partly from the steam to thewire mesh, together with a secondary transfer of this heat from the wiremesh tothe water.

It lwill b e apparent that in the process of evaporation of water inthe'desuperheater, particularly with natural sources of supply, it isinevitable that some scale may form on the desuperheater element.Normally the extreme temperature ranges which the apparatus encounterswill detach this scale from the wire mesh by the difference in expansionbetween the scale and wire.. The present construction, however, makes 1tpossible to effectively remove any remaining scale periodically as maybe desired, by simply removing the cartridge bodily and then shaking thechain or tape of wire mesh. Thereafter the mesh may be again lapped orfolded into position and the cartridge inserted in the desuperheaterchamber.

Certain advantages of the present invention arise from the provision ofa desuper- `heater embodying a porous body or a body pervious to thepassage of steam, together with means for supplying water in such mannerthat an efiicient contact between the water and steam is insured.

Other advantages arise from the provision of means for effectivelybringing the desuperheating water into contact with superheated steam insuch manner that the superheated steam is reduced to a condition ofsaturation. .l

Still other advantages arise from the construction permitting theremoval of the cartridge and cleaning of the parts as may be desired.

I claim:

1. In the method of desuperheating steam, the steps comprising providinga body of water in broken up condition intersecting the path of iow ofthe superheated steam, and breaking up the steam and bringing it intocontact with the -Water while both are in broken up condition.

2. In the method of desuperheating steam, the steps comprising providinga body of water in broken up condition intersecting the path of flow ofthe steam, breaking up the steam and bringing the steam and water whilein broken up condition into contact with each other, and continuouslysupplying water to an amount sulicient only to substantially reduce thesuperheat in the steam to a condition of saturation.

3. In the method of treating steam, the

4. ln the method of treating steam, the steps comprising passing thesteam in broken up condition through a plurality of tor'tuousv paths,and supplying water to thesteam while traveling through said aths.

5. "In the method 'o treatin steam, the

steps comprising maintaining a lm of water in steam intersectingposition by capillary `action on the water, and then passing th steamthrough said film.

6. In thermethod of treating steam, the

' steps comprising providing al plurality ,of

tortuous How paths for the steam, maintaining desuperheating water inintimate relation to said flow paths by ca illary action, and passinsteamthrou'gh sai paths in contact with t e water.

7. In the method of desuperheg, lthe steps comprising breaking the steam*intoirf 1 regular bodies and producing a random How'. of such bodies inconfined spaeeg and supply-

